Quantification of Micro-Crack Density for Fiber Based Composites

This paper describes a method for quantifying defects in fiber based composite materials created during the fabrication process. The defects include voids that arise during manufacturing, micro-cracks produced during cure, and delaminations which occur between lamina. In this method, photomicrography technology is used in conjunction with computer aided design (CAD) software. The photomicrographs, stored as bitmap images, provide a visualization of the bond behavior between the fiber and the resin materials. The CAD software transforms each bitmap image into a two-dimensional work space where the areas of the defects are computed by tracing them using a closed polygon feature. Micro-crack density measurements are made by dividing the sum of the individual micro-crack areas by the total specimen area. The approach is applied to measure the micro-crack densities in materials used for ablative nozzle applications.